FIG. 21 is a diagram showing a safety apparatus for an elevator disclosed in U.S. Pat. No. 6,170,614. In the safety apparatus 1000, a car position detected by a car position detecting device 1002 is transmitted to a microprocessor 1006 of a speed governor 1004. The microprocessor 1006 calculates a car speed on the basis of position information of a car. A car speed thus calculated is compared with an overspeed detection level (speed limit) stored in a memory 1008 of the speed governor 1004. If the car speed exceeds the overspeed detection level, a signal is transmitted from the speed governor 1004 to an emergency stop device 1010. Then, the emergency stop device 1010 operates, so that the car makes an emergency stop.
The elevator apparatus disclosed in this U.S. patent stores a plurality of overspeed detection levels in the memory, and the microprocessor selects one overspeed detection levels from among the plurality of overspeed detection levels thereby making it possible to change the overspeed detection level. As criteria for selecting the overspeed detection level, car position information to be inputted to the microprocessor, specification data of the elevator stored in the memory and so on are exemplified.
In the elevator apparatus disclosed in the Patent, for one example of the means for detecting the car position, an ultrasonic position sensor is described. However, an ultrasonic wave has the following drawbacks: it interferes with other devices installed in an elevator shaft and is liable to be affected by them. Also, the measurable distance by the ultrasonic wave is limited. Further, it is difficult to accurately determine in advance a dimension of the elevator shaft, the distance between floors and so on. This requires an operation to store these data in the memory by on-the-spot adjustment. Furthermore, over long-time use of the elevator apparatus results in the occurrence of an error in the sensor, or a change in the dimensions of a building causes displacement of the sensor. Therefore, it is required to take countermeasures, such as changing data stored in the memory, to compensate the error or displacement.
Next, FIG. 22 is a diagram showing an elevator apparatus disclosed in Japanese Publication No. 9-165156 (A). The elevator apparatus 1022 has an elevator car 1014, a winding device 1016 serving as a car driving mechanism, a winding wire 1018, a balance weight 1020, safety switches 1022-1028, an emergency stop device 1030, a guide rail 1032, a basic drive mechanism 1034, a cable 1036, and a trigger 1038. In this construction, when the car 1014 descends or ascends, a travel parameter given to the winding device 1016 is also provided to the basic drive mechanism 1034. Therefore, the car 1014 and the trigger 1038 of the basic drive system 1034 adjacently travel in parallel. If a difference takes place between their travels, and the trigger 1038 comes in contact with any one of the safety switches 1022-1028, the trigger 1038 controls the winding device 1016 in accordance with the switch with which it comes in contact, or drives the emergency stop device 1030, so that the car 1014 stops ascending or descending.
In the elevator apparatus disclosed in Japanese Patent Publication No. 9-165156 (A), a deviation between a drive speed command value and an operation speed of the car is detected, and if the deviation exceeds a predetermined margin, the emergency stop device is operated. For that reason, the trigger, which operates the safety switches positioned on the side of the car, is fixed to a cable of the basic drive mechanism and moved in a manner so as to travel in parallel with the car. However, the trigger is liable to be affected by an operation error of the basic drive mechanism with accompanying long-time use of the elevator apparatus, accumulation of displacement due to slippage etc. between the cable and a sheave that supports the cable, or a change with time in the diameter of the sheave and so on due to wear of the sheave that transmits power to the cable.